The development of thin stylish cellular phones having sound functions such as music reproduction or a hands-free function as commodity values has been actively conducted. In this situation, there is strong demand for electro-acoustic transducers that are made small and thin and that has a high-quality sound. In addition, the development of thin piezoelectric electro-acoustic transducers to replace electrodynamic electro-acoustic transducers of the related art has been actively conducted. The piezoelectric electro-acoustic transducers reproduce a sound wave using an expansion and contraction motion of a piezoelectric element. For this reason, there is an advantage in a reduction in the thickness thereof as compared to an electrodynamic electro-acoustic transducer constituted by a magnet or a voice coil.
At present, various types of electro-acoustic transducers described above have been proposed (Patent Documents 1 to 3).